HR: 0800h
AN: G21A-0140    [Abstracts]
TI: GPS/Acoustic seafloor positioning off the northeastern Japan with a new acoustic system
AU: * Funakoshi, M
EM: m.ito@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578 Japan
AU: Fujimoto, H
EM: fujimoto@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578 Japan
AU: Hino, R
EM: hino@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578 Japan
AU: Miura, S
EM: miura@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578 Japan
AU: Osada, Y
EM: osada@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578 Japan
AU: Kuwano, A
EM: kuwano@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ., Aoba-ku, Sendai, 980-8578 Japan
AU: Sweeney, A
EM: aaron@jamstec.go.jp
AF: JAMSTEC , 2-15 Natsushima, Yokosuka, 237-0061 Japan
AU: Kawakami, T
EM: KYU03656@nifty.com
AF: Kaiyo Denshi Co., Ltd., 2-17-3 kasumigaseki-kita , Kawagoe, 350-1109 Japan
AU: Yabuki, T
EM: tetsuichirou-yabuki@kaiho.mlit.go.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1 Tsukiji Chuo-ku, Tokyo, 104-0045 Japan
AU: Fujita, M
EM: masayuki-fujita@kaiho.mlit.go.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1 Tsukiji Chuo-ku, Tokyo, 104-0045 Japan
AU: Kawai, K
EM: kohji-kawai@kaiho.mlit.go.jp
AF: Hydrographic and Oceanographic Department, Japan Coast Guard, 5-3-1 Tsukiji Chuo-ku, Tokyo, 104-0045 Japan
AB: We developed a seafloor positioning system combining kinematic GPS (KGPS) and precise underwater acoustic ranging to investigate dynamics in the subduction of the Japan Trench. The acoustic system for medium water depths is simple enough to use a signal with a single frequency of 10kHz. We deployed 3 precision acoustic transponders (PXPs) off Miyagi Prefecture, where the next earthquake is suspected. In this talk, we present results of GPS/A experiments carried out using the PXPs in August and October, 2003, and in August 2004. We used a towed buoy with 3 or 4 GPS receivers an acoustic ranging system for GPS/A observation in August 2003 and 2004. In October, we put the transducer on a post in the stern of a vessel and determined its location by using a GPS antenna and a motion sensor on the top of the post. Obtained dataset consists of three elements: position of a seasurface transducer, two-way travel times between the transducer and the PXPs, and the sound velocity structure. We calculate the two-way travel time of an acoustic signal of 18.6ms between the transducer and a PXP with a resolution of 0.002ms (= 1.5mm in ranging), by taking correlation between the transmitted and the received signals. During the experiments, we deployed CTD one hour before the buoy operation to measure salinity, temperatures, and pressure. We also performed XBT casts every 1-3 hours to measure temperature. Sound velocity structure is then estimated by using the empirical law by Del Grosso (1974) from these data. There are 2 steps to estimate the location of the center of the PXP array. At first, we estimate the positions of each PXP using data collected while the buoy shifted around each PXP. In the second step, we determine the center of the PXP array using the data collected near the pre-defined center. In order to remove the influence of a ocean tide, we use the tide prediction program called NAOTIDE-J (Matsumoto et al., 2000). The number of shots which can be used in the analysis in the center was only 14 for shortage of the observation period. However, analyzing with this small number of shots, the accuracy of the central position of the array are about 5-6cm in standard deviation. We could carry out GPS/A observation for 8 hours on a vessel in October 2003 and 73 hours on a buoy in August 2004. These data are under processing.
DE: 8110 Continental tectonics--general (0905)
DE: 1206 Crustal movements--interplate (8155)
DE: 1208 Crustal movements--intraplate (8110)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting